Print Email Facebook Twitter Concentration and flow velocity measurements in a local scour hole Title Concentration and flow velocity measurements in a local scour hole Author Hoffmans, G.J.C.M. Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 1990-01-01 Abstract Flume experiments with small Froude numbers have been carried out to study the concentration field in a local scour hole without supply of sediment load. The measuring results will be used to check the validity of the two dimensional scour model DUCT-SUSTRA. The objective of the experiments was to measure the concentrations at various locations in the flume above a movable bed of fine sand (d_50 = 165 m*10^-9). The experimental set-up and the equipment and procedures of the measurements are described in chapter 3. The flow velocities were measured with an electromagnetic flow meter (EMS). The sediment concentrations were determined from water-sediment samples, which were collected by siphoning (free fall method). The experimental results such as the bed-configuration profiles, the sediment concentrations and the flow velocities are presented in chapter 4. The time, in which the maximum scour depth in the experiments is equal to the initial flow depth, is compared with the time predicted by an analytical scour formula. CONCLUSIONS Based on bed-configuration profiles at the flume axis and halfway between the flume axis and the side it can be deduced that the scour process was mainly two-dimensional. The slope of the scour hole was smooth, while ripples were formed downstream of the re-attachment point, where a new wall layer develops. The equivalent roughness height, which is defined as the height from the averaged bed level till the top of the ripples, was approximately 1.5 cm. The coefficient a, which represents a dimensionless scour factor involving the velocity distribution and the influence of the turbulence intensity due to the geometry of the structure, is not unambiguous and varied from 1.75 to 2.15 for the four runs (run C60). This reflects a difference of about a factor three for the time, in which the maximum scour depth is equal to the initial flow depth. Subject scourflow velocityDUCT-SUSTRAexperimentscour hole To reference this document use: http://resolver.tudelft.nl/uuid:570b81ef-15a7-4b87-ba74-dc9c6d1cb84e Publisher TU Delft, Department of Hydraulic Engineering Source Report no. 4-90 Part of collection Institutional Repository Document type report Rights (c) 1990 TU Delft, Department of Hydraulic Engineering Files PDF Hoffmans1990.pdf 18.33 MB Close viewer /islandora/object/uuid:570b81ef-15a7-4b87-ba74-dc9c6d1cb84e/datastream/OBJ/view